How can i change the master background of a Powerpoint?

Answer 1

Go to the View Menu.
Select Master and then Slide Master.
The master of yours slides will appear.
Do all the changes that you want to and then click on Close Master View.

If you want to change the background of one slide (or all) without going to the master... just left click on the slide... select Background and change it as you want it to.

Good luck

Answer 2

you go into control panel .you click on theme and art after that you pick an task.